My client's online store uses the Authorize.net SIM payment gateway (off-site payment gateway), so when placing a credit card order, a customer is redirected to an external secure page hosted by https://secure.authorize.net/etc... When a customer checkout using Firefox, after they submit their credit card details on the external secure page, they get a popup window saying "Security Warning -- The information you have entered on this page will be sent over an insecure connection and could be read by a third party. Are you sure you want to send this information?". I'm not sure how long this has been happening, but customers have only been complaining about it recently.
I'm at a loss for what to do to fix this. Is it an Expresso Store issue? An Authorize.net issue? An SSL issue?
Any help would be greatly appreciated.
- EE v2.9.2
- Store v2.5.1